This invention relates to the re-refining of lubricating oil and more particularly to passing the lubricating oil through a bed of oil shale to enhance the re-refining and the conversion of kerogens in the shale oil.
The increasing concern for conservation of petroleum reserves and the best use of products derived from them has engendered renewed interest in re-refining lubricating oils. The re-refining of used lubricating oils has also been practiced to reduce the ecological impact of disposal. Used lubricating oils are contaminated with water, debris from wear of metal parts and decomposition products of spent additives in the oil.
Removing these contaminants to produce a reusable crude stock is desirable. Lubricating oils are manufactured from special crude oils. Such crude oils are not very common and for a crude oil to be designated as a "lube crude", rigorous standards of yield versus treat conditions have to be met. A lube oil base stock has to meet other rigorous standards before it is considered suitable for an economically and commercially viable application in lube formulations. The recovery of these lubricating base stocks is desirable.
As is known, additives and combinations of additives are mixed with base stock to meet operational requirements of viscosity index, oxidation stability, demulsification behavior, and so on. In service, the additives which are usually the minor component of the total mixture, become spent and the lubricating oil loses the properties required for that particular service. However, the major portion of the base stock remains unchanged and it can be recovered by removing the metal debris and other contaminants.
"NEW RE-REFINING TECHNOLOGIES OF THE WESTERN WORLD" M. L. Whisman, Manual of the Amer. Soc. of Lubrication Engineers, Vol. 35, 5, pp. 249-253, summarizes the prior art techniques of re-refining lubricating oil. This article refes to U.S. Pat. Nos. 3,773,658, 3,919,075, 3,879,282, 3,930,988, and 4,073,719 as showing typical processes for re-refining lubricating oils. In general, the prior art techniques produce a usable base stock and sludge which must be disposed of.
In a separate technology, useful hydrocarbons are recovered from oil shale. U.S. Pat. No. 3,574,087, for example, shows oil shale being fed to a retort for the conversion of kerogens to hydrocarbons. This conversion is a difficult procedure which can be enhanced by doing it in the presence of hydrogen donor compounds.